Outer envelopes with insert lamps have wide household and industrial application. The outer envelopes protect the insert lamps from harmful outside effects and impacts, make the light of the insert lamp diffuse and more uniform when their surface is suitable formed, and lend the light source an advantageous aesthetical appearance. The outer envelopes are also used with compact fluorescent lamps. Most recently, compact fluorescent lamps retrofits for an incandescent lamp have been designed. These lamps are provided with bulb-shaped outer envelope that has dimensions close to those of incandescent lamps, and imitate an aesthetic appearance of incandescent lamps.
U.S. Pat. No. 4,527,089 discloses a compact fluorescent lamp comprising multiple, individual tubes mechanically formed into an assembly and inserted into an outer envelope. The individual open-ended tubes are connected to each other through an arc directing means to form a continuous arc path. The outer envelope has a cylindrical shape, is sealed and includes an arc generating and sustaining medium such as an atmosphere of mercury and argon. The electric wires of the fluorescent lamp as lead-in wires are led through a flare that serves as a sealing element of the cylindrical outer envelope. The ballast circuit providing energy for the fluorescent lamp is situated outside the outer envelope and therefore it requires special contact elements and arrangement.
U.S. Pat. No. 4,600,856 describes a compact low-pressure arc discharge lamp with multiple tubes frictionally fitted into apertures in a base plate. The base plate is held in a fixed position inside the sealed outer envelope but there is no built in ballast in the outer envelope or bulb. A CFL of such a construction has to be connected to outer ballast, which requires external electric connections and a special connection means to connect the ballast to a power supply.
U.S. Pat. No. 6,064,155 discloses a fluorescent lamp with an outer envelope having an external shape of an incandescent lamp on a standard Edison-type base. The discharge tube is wound in a coil around the axis of the envelope and is disposed within the outer envelope. Ballast is also disposed within the outer envelope. A heat shield is disposed between the lamp and the ballast to thermally isolate the lamp from the ballast, whereby heat from the lamp will not adversely affect the ballast. Although this lamp is provided with integrated ballast inside the outer envelope, it is not disclosed and therefore it is not clear from this document how the lamp and the ballast circuit components are positioned inside the relatively small inner space of the outer envelope and how the electrical connection between the lamp electrodes and the ballast circuit or between the ballast circuit and the base is established.
There is a need for bulb-shaped outer envelopes that provide sufficient space for lamps and components of the control gear of lamps while preserve the size of the envelope of usual incandescent lamps. Similarly, there is a need for a self-ballasted compact fluorescent lamp that has a bulb-shaped outer envelope, can replace usual incandescent lamps, can be manufactured easily, and has high lumen output and relatively small size.